One of the most obviously bogus pit bull myths is the old story that pit bulls never start a fight, but always finish it.
Let's correct the record here: pit bulls always start the fight. And they will always finish it too, so long as the victim is unable, unwilling or unequipped to fight back effectively. But not being known for high intelligence, pit bulls sometimes pick a hard target.
The following video is an interesting study. Spoiler: The owners manage to break up the fight before any serious lasting damage is done.
The pit bull clearly wanted to fight the big dog, an American Akita, but didn't seem willing to tackle him head on, and kept trying to go outside his field of vision to bite him. The Akita is not looking for a fight, but also does not suffer fools gladly. He keeps warning the pit bull away with growls, bluff charges and air snaps. Finally, in jumping on the Akitas back to bite him, the pit bull transitions from nuisance to threat, and the Akita goes all in, knocking the pit bull down, dragging it around by the scruff of the neck, putting it on it's back and roughing it up.
We've seen far worse outcomes than this for pit bulls that attack, e.g. livestock guardian breeds. Unfortunately, pit bulls rarely attack American Akitas, Kangals, or 160 pound Great Pyrenees, apparently preferring much softer targets. Had the intended victim in the video link above been the typical chihuahua, shih-tzu, yorkie or mini-poodle, it's likely that the poor little dog on the receiving end would be dead, or nearly so.
The behavior of a breed designed to kill dogs for sport will be very different from a breed designed to, say, point, herd, retrieve, or guard. The very real, hard-wired genetic differences are not something that should be dismissed out of hand. You ignore DNA at your own peril.
For more info, check out the informative article below about dog language and signals, and how pit bulls differ from other dogs in this regard - starting fights even when we don't think they're starting them.
Language of dogs, normal and psychopathic